No need to panic, it's probably pretty simple. It sounds like your system is full of air and just needs to be bled. You've probably bled all the pressure out of the system, so you'll need to re-pressurize it, then bleed the radiators again, then pressurize again, bleed again, until all the air is gone.
Look at your boiler, there should be a pressure gauge on it. It should have a green arc, and maybe a yellow ark before having a red ark. Most likely green will go up to 2 bar(29 psi). Right now the needle is probably on the low end of the scale.
You'll need to find your pressurization valve, and open it until you get some pressure. The pressurization valve is between your home's water supply and the boiler, all you need to do is open it until you get about 1.2 to 1.5 bar and then close it. If you cannot find the valve see if you can find the manual, or just ask a neighbor who seems handy. It's very simple and you shouldn't need to pay anyone to do it.
Be careful not to over-pressurize the system, turn off the pressurization valve before the needle goes into the red.
Other than looking for hidden bleeders (i.e. I have one where the baseboard cover needs to be removed to reveal the bleeder) and bleeding any bleeders that you can find, you may need to swear at whoever put in the new radiators and retrofit bleeders where they are missing.
There is often an automatic bleeder/vent on or just after (in which case it's often on a big cast iron "air separator" that may have an expansion tank hung off its bottom) the boiler, since in theory any dissolved air will be most prone to come out of solution where it's hottest - if that becomes clogged or otherwise inoperable (they don't last overly long) air may migrate elsewhere more than it would if that was working. Sometimes people see a dribble from these and close down the cap on the "tire fill valve" rather than replacing them - which renders them inoperable. I think it's bad practice to depend on that for bleeding the whole system.
Given how anemic circulator pumps are when faced with air bubbles, the only other way of getting that loop clear would be to open the boiler fill and open a drain on that loop, so that the fill water can push the bubble through to the drain - but then you have new water in the system, and some air will come out of that.
Best Answer
What worked for me were Q-tips. I worked them around the surfaces of each fin and attempted to do the same with the pipe to which the fins are attached. The shaft of the Q-tips were long enough to reach beyond the top to bottom of the fins, and the tips were wide enough to touch both surfaces of adjacent fins without damaging them. The process was not fast but it was effective. The clean-up was with a vacuum cleaner. Subsequently I sprayed the surfaces with the Clorox cleaner/bleach product and again ran Q-tips over the fins. Based on the cleanliness of the tips after use, the process did not seem to add much value.